The invention relates to systems and methods for testing electrochemical systems. The invention has application to testing electrochemical batteries, fuel cells and other electrochemical systems. The invention may be embodied, for example, in battery testers.
It can be necessary to test electrochemical systems to evaluate their condition. For example, electrochemical batteries used in critical applications need to be tested periodically to ensure that they will be able to function properly when needed. Testable characteristics of electrochemical batteries may include: state of health (SoH), state of charge (SoC), cold cranking amperes (CCA), cranking amperes (CA), marine cranking amperes (MCA), reserve capacity, capacity and others.
There exist various battery testing methods. Some of these methods are undesirably time consuming. Others require the battery being tested to be discharged, so that during testing the battery is not available for service. Other tests are undesirably inaccurate.
There is a need for new methods and apparatus for testing electrochemical systems, such as electrochemical batteries, which ameliorate at least some disadvantages of the prior art.
The invention relates to methods and apparatus for testing electrochemical systems.
One aspect of the invention provides methods for testing an electrochemical system. The methods comprise: obtaining complex impedance data for the electrochemical system at a plurality of frequencies; fitting the complex impedance data to a plurality of models of the electrochemical system to obtain a set of fitted parameters, the set of fitted parameters comprising at least one fitted parameter corresponding to each of the models; and, deriving a value for a characteristic of the electrochemical system based upon one or more parameters selected from the set of one or more fitted parameters. The models may include electronic equivalent circuit models.
The electrochemical system may comprise a battery, fuel cell, surface coating, electrolytic capacitor, or the like.
Another aspect of the invention provides a method for deriving a characteristic of an electrochemical system. The method comprises extracting impedance data from the electrochemical system at a plurality of discrete frequencies; mathematically fitting a plurality of models to the extracted impedance data to obtain a set of fitted parameters; and, inferring the characteristic based on one or more parameters selected from the set of fitted parameters.
A further aspect of the invention provides apparatus for testing electrochemical systems. The apparatus comprises: a measuring circuit connectable to measure responses of the electrochemical system to an excitation signal at a plurality of frequencies; and a data processor configured to: obtain complex impedance data for the electrochemical system from the measuring circuit; fit the complex impedance data to a plurality of models of the electrochemical system to obtain a set of fitted parameters, the set of fitted parameters comprising at least one fitted parameter corresponding to each of the models; and, derive a value for a characteristic of the electrochemical system based upon one or more parameters of the set of fitted parameters.
A further aspect of the invention provides apparatus for testing an electrochemical system. The apparatus comprises means for extracting impedance data from the electrochemical system at a plurality of discrete frequencies; means for mathematically fitting a plurality of models to the extracted impedance data to obtain a set of fitted parameters; and, means for inferring a characteristic of the electrochemical system based on one or more parameters selected from the set of fitted parameters.
Another aspect of the invention provides a machine readable medium carrying data. The data comprises a set of instructions which, when executed by a data processor, cause the data processor to perform a method of testing an electrochemical system. The method comprises: obtaining impedance data for the electrochemical system at a plurality of frequencies; fitting the impedance data to a plurality of models of the electrochemical system to obtain a set of fitted parameters, the set of fitted parameters comprising at least one fitted parameter corresponding to each of the models; and, deriving a value for a characteristic of the electrochemical system based upon one or more parameters selected from the set fitted parameters.
Further aspects of the invention and features of specific embodiments of the invention are described below.